With　the　rapid　development　of　space　exploration　and　new　energy　vehicles,　it　is　urgent　to　build　ultra-wide　temperature　multilayer　ceramic　capacitors　(UWT　MLCCs)　to　match　electronic　circuits　that　can　withstand　harsh　environmental　conditions.　Relaxor　ferroelectrics　with　diffuse　phase　transition　feature　are　potential　dielectrics　for　the　construction　of　UWT　MLCCs.　However,　how　to　ensure　high　dielectric　constant　together　with　low　dielectric　loss　in　the　wide　temperature　region　is　still　a　big　challenge.　Here,　the　above　difficulties　are　addressed　by　tailoring　the　combination　types　of　polar　nanoregions　(PNRs)　in　the　(1-x)　(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xNaTaO3　(NBT-KBT-xNT)　system.　Compared　with　PNRs　types　of　P4bm　+　R3c　and　P4bm　+　Pbnm,　the　combination　type　of　P4bm　+　Pbnm　+　R3c　PNRs　in　NBT-KBT-0.31NT　is　the　most　beneficial　to　obtain　comprehensive　excellent　dielectric　performance　because　it　can　balance　the　relationship　between　high　dielectric　constant　and　temperature　stability　over　a　wide　temperature　region.　Further,　by　optimizing　the　laminating　pressure　and　co-firing　temperature　to　realize　a　tight　interfacial　structure　between　the　dielectric　layer　and　the　Pt　inner　electrode,　a　record-high　dielectric　constant　(εr　=　(907%　±　15%))　together　with　low　dielectric　loss　(tanδ　≤　0.025)　is　achieved　over　an　ultra-wide　range　from　−61　°C　to　306　°C　for　NBT-KBT-0.31NT　MLCC,　demonstrating　that　tailoring　the　combination　types　of　PNRs　is　a　powerful　strategy　in　designing　UWT　MLCC　dielectrics.　©　2023　The　Authors